This invention concerns an arrangement of oil cylinders for a plastic injecting machine. More particularly, the present invention is directed to an arrangement of four oil cylinders moving a material injecting cylinder, and in such a position to be far away enough from the material injecting cylinder to prevent the oil seals of the four oil cylinders from being heated by hot electric heaters of the material injecting cylinders used during injecting operation.
A conventional plastic injecting machine, shown in FIG. 5, has a double injecting oil cylinder base 1 on a work table 6, a double oil cylinder 2 consisting of a large diameter cylinder and a small diameter cylinder combined in series at a left and a right side of the oil cylinder base 1. The double oil cylinders 2 extend forward in parallel with a material injecting cylinder.
When in injecting operation, an oil motor 3 is started to rotate a screw rod in a bearing base 4, and an oil cylinder 5 is started to move the oil cylinder base 1 forward, with the piston rods of the two double oil cylinders 2 also moved forward at the same time with the bearing base 4. When the piston rods are retracted, the bearing base 4 is also moved back together therewith. Though the two double oil cylinders 2 can operate with proper pressure and speed needed for displacing the plastic material, they are located very near to the material injecting cylinder. The material injecting cylinder is encompassed by electric heaters, so the oil seals provided in the two double oil cylinders 2 are heated by those heaters to more than 250.degree. C. during the injecting operation. Since common oil seals have a normal temperature resistance of 95.degree. C., their service life will be shortened by exposure to such a high operating temperature.